[hibernate-dev] Attribute converters and dirty checks

[Vlad Mihalcea]

Hi,

I think it should be symmetric because if that property takes part in the
Object equality (equals/hashCode),
then the entity will not be equal to itself after you persisted and loaded
it again from the database.

final Event event = doInJPA(entityManager -> {
    Event _event = new Event();
    entityManager.persist(_event);
    return event;
});

doInJPA(entityManager -> {
    assertEquals(event, entityManager.find(Event.class, event.getId()));
});

This can be a problem if the Entity is part of a Set/Map too.

Vlad

On Thu, Jan 7, 2016 at 3:15 PM, Gunnar Morling <gunnar at hibernate.org> wrote:

> Hi,
>
> I have an entity with an attribute whose value is converted by means
> of an attribute converter. The converter operations are not symmetric,
> i.e. it's not guaranteed that
>
>     value.equals( convertToEntityAttribute( convertToDatabaseColumn( value
> ) ) )
>
> is true.
>
> Question 1: Is such converter valid, or is it a requirement that its
> operations are symmetric?
>
> If this converter is valid, then I am curious whether the following
> optimization could be applied.
>
> Currently, the dirty checking is based on equality comparison of the
> attribute value. During persist a deep copy of the entity attribute
> array is made, which does the forth-and-back conversion above. If the
> converter isn't symmetric, this may yield a value which is different
> from the one in the entity attribute.
>
> Then at dirty check, the entity attribute is compared to that value
> resulting from deep-copying, causing the property to be considered
> dirty, although the value to be stored in the database actually is the
> same. Subsequently, an UPDATE will be issued which contains the same
> column value as the previous INSERT.
>
> So, question 2: Would it be feasible to do the dirty check based on
> the converted value?
>
> Thanks,
>
> --Gunnar
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